The present invention relates to a method for etching semiconductor substrates in etching chambers, and of cleaning the etching chambers.
In the manufacture of integrated circuits, silicon dioxide, silicon nitride, polysilicon, metal silicide, and monocrystalline silicon on a substrate, are etched in predefined patterns to form gates, vias, contact holes, trenches, and/or interconnect lines. In the etching process, a patterned mask layer composed of oxide or nitride hard mask or photoresist, is formed on the substrate using conventional methods. The exposed portions of the substrate between the patterned mask are etched by capacitive or inductively coupled plasmas of etchant gases. During the etching processes, a thin polymeric etch residue deposits on the walls and other component surfaces inside the etching chamber. The composition of the etch residue depends upon the composition of vaporized species of etchant process gas, the substrate material being etched, and the mask or resist layer applied on the substrate. For example, when tungsten silicide, polysilicon or other silicon-containing layers are etched, silicon-containing gaseous species are vaporized or sputtered from the substrate, and etching of metal layers results in vaporization of metal species. In addition, the resist or mask layer on the substrate is also partially vaporized by the etchant gas to form gaseous hydrocarbon or oxygen species. The vaporized or gaseous species in the chamber condense to form polymeric byproducts composed of hydrocarbon species from the resist; gaseous elements such as fluorine, chlorine, oxygen, or nitrogen; and elemental silicon or metal species depending on the composition of the substrate being,etched. The polymeric byproducts deposit as thin layers of etch residue on the walls and components in the chamber. The composition of the etch residue layer typically varies considerably across the chamber surface depending upon the composition of the localized gaseous environment, the location of gas inlet and exhaust ports, and the chamber geometry.
The compositional variant, non-homogeneous, etch residue layer formed on the etching chamber surfaces has to be periodically cleaned to prevent contamination of the substrate. Typically, after processing of about 25 wafers, an in-situ plasma xe2x80x9cdry-cleanxe2x80x9d process is performed in an empty etching chamber to clean the chamber. However, the energetic plasma species rapidly erode the chamber walls and chamber components, and it is expensive to often replace such parts and components. Also, erosion of the chamber surfaces can result in instability of the etching process from one wafer to another. The thin compositional variant etch residue can also make it difficult to stop the in-situ plasma clean process upon removal of all the residue, resulting in erosion of the underlying chamber surfaces, and making it difficult to clean the hard residue off all the chamber surfaces. For example, the etch residue formed near the chamber inlet or exhaust often has a high concentration of etchant gas species than that formed near the substrate which typically contains a higher concentration of resist, hard mask, or of the material being etched.
It is difficult to form a cleaning plasma that uniformly etches away the compositional variants of etch residue. Thus after cleaning of about 100 or 300 wafers, the etching chamber is opened to the atmosphere and cleaned in a xe2x80x9cwet-cleaningxe2x80x9d process, in which an operator uses an acid or solvent to scrub off and dissolve accumulated etch residue on the chamber walls. To provide consistent chamber surface properties, after the wet cleaning step, the chamber surfaces are xe2x80x9cseasonedxe2x80x9d by pumping down the chamber for an extended period of time, and thereafter, performing a series of runs of the etch process on dummy wafers. The internal chamber surfaces should have consistent chemical surfaces, i.e., surfaces having little or no variations in the concentration, type, or functionality of surface chemical groups; otherwise, the etching processes performed in the chamber produce widely varying etching properties from one substrate to another. In the pump-down process, the chamber is maintained in a high vacuum environment for 2 to 3 hours to outgas moisture and other volatile species trapped in the chamber during the wet clean process. Thereafter, the etch process to be performed in the chamber, is run for 10 to 15 minutes on dummy wafers, or until the chamber provides consistent and reproducible etching properties.
In the competitive semiconductor industry, the increased cost per substrate that results from the downtime of the etching chamber, during the dry or wet cleaning, and seasoning process steps, is highly undesirable. It typically takes 5 to 10 minutes for each dry cleaning process step, and 2 to 3 hours to complete the wet cleaning processes. Also, the wet cleaning and seasoning process often provide inconsistent and variable etch properties. In particular, because the wet cleaning process is manually performed by an operator, it often varies from one session to another, resulting in variations in chamber surface properties and low reproducibility of etching processes. Thus it is desirable to have an etching process that can remove or eliminate deposition of etch, residue on the chamber surfaces.
In semiconductor fabrication; yet another type of problem arises in the etching of multiple layers of materials that have similar constituent elements, for example, silicon-containing materials such as tungsten silicide, polysilicon, silicon nitride, and silicon dioxide. With reference to FIGS. 1a and 1b, a typical multilayer polycide structure on a semiconductor substrate comprises metal silicide layers 22 deposited over doped or undoped polysilicon layers 24. The polycide layers are formed over silicon dioxide layers 26, and etched to form the etched features 30. In these multilayer structures, it is difficult to obtain a high etching selectivity ratio for etching the metal silicide layer relative to the overlying resist layer 28, or the underlying polysilicon layer 24. It is especially desirable have high etching selectivity ratios for polycide structures that have a non-planar and highly convoluted topography, where the portion of the conformal metal silicide layer 22 between the etched features is thicker than the portion of the metal silicide layer 22 on top of the etched features (not shown). At a certain time during the etching process, the thinner metal silicide layer is etched through and etching of the underlying polysilicon layer begins, while the thicker metal silicide layer 22 is still being etched. This requires that the polysilicon layer 24 be etched sufficiently slowly relative to the rate of etching of the metal silicide layer, that the entire polysilicon layer 24 below the thinner metal silicide layer is not etched through, before completion of etching of the thicker portions of the metal silicide layer 22. Thus, it is desirable to etch the metal silicide layer 22 at a faster rate relative to the rate of etching of the polysilicon layer 24. The same problem arises in the etching of a mask layer of silicon nitride 32, on a very thin silicon dioxide layer 34, prior to forming trenches in a substrate comprising silicon 36, as for example shown in FIGS. 1c and 1d. The etched trenches 38 are used to isolate active MOSFET devices formed on the substrate. The etching selectivity ratio for etching silicon nitride relative to silicon dioxide has to be very high to stop on the silicon dioxide layer without etching through the layer.
High etching selectivity ratios are obtained by using process gas compositions that etch the different silicon-containing materials at significantly different etching rates, which depend upon the chemical reactivity of the particular process gas composition with a particular layer. However, etching metal silicide layers with high selectivity to polysilicon, or etching silicon nitride layers with high selectivity to silicon dioxide layers, is particularly difficult because both materials contain elemental silicon and most conventional etchant plasmas etch the silicon containing layers to form gaseous SiClx or SiFx species. Thus, it is difficult for the etchant plasma to chemically distinguish and preferentially etch the metal silicide layer 22 faster than the polysilicon layer 24, and the silicon nitride layer 32 faster than the silicon dioxide layer 34. This problem is further exacerbated because the etchant residue formed on the chamber sidewalls also contains silicon dioxide, and attempts to remove the etchant residue during the polycide etching process, result in substantially lowering the rate of etching selectivity ratio of these layers.
Thus it is desirable to have an etch process that reduces formation of etch residue deposits in the etching chamber. It is also desirable that the etch or cleaning gases do not to erode the exposed surfaces in the chamber. It is further desirable to have an etch or cleaning process that restores the original chemical reactivity and surface functional groups of the chamber surfaces. It is further desirable for the chamber cleaning process to remove chemically adhered etch residue layers having variable thickness and stoichiometry, without excessive erosion of underlying chamber surfaces. It is also desirable to have an etch process for removing etch residues generated by etching multiple layers of materials, for example, silicon dioxide containing etch residues during etching of tungsten silicide on polysilicon layers, or silicon nitride on silicon dioxide layers, without sacrificing their etching selectivity ratio.
In one aspect of the invention, a substrate processing method comprises placing a substrate in a chamber, the substrate having a layer thereon, providing an energized etchant gas in the chamber to etch substantially through the layer while providing an energized cleaning gas to substantially clean the chamber, and repeating the steps.
In another aspect of invention, a substrate processing method comprises placing a substrate in a chamber, the substrate having a layer thereon; providing an energized etchant gas in the chamber to etch the layer, the energized etchant gas being provided before etchant residue from the layer has been formed on the chamber surfaces, during the previous step, providing an energized cleaning gas to substantially clean the chamber; and repeating the steps.
In another aspect of the invention, a substrate processing method comprises placing a substrate in a chamber, providing a first energized etchant gas in the chamber to etch the substrate, providing a second energized etchant gas in the chamber to etch the substrate, and providing a burst of energized cleaning gas during the providing of the first energized etchant gas and/or the second energized etching gas to substantially clean the chamber.
In another aspect of the invention, a substrate processing method comprises placing a substrate in a chamber, providing an energized etchant gas in the chamber to etch the substrate while simultaneously providing a burst of energized cleaning gas to substantially clean the chamber surfaces, and repeating the steps.
In another aspect of the invention, a substrate processing method comprises placing a substrate in a chamber, providing a first energized etchant gas in the chamber to etch the substrate, the first energized etchant gas comprising a chlorine-containing gas or a bromine-containing gas, providing a second energized etchant gas in the chamber to etch the substrate, and during the providing of the first energized etchant gas and/or the second energized etching gas, providing an energized cleaning gas to clean the chamber surfaces.
In another aspect of the invention a substrate processing method comprises placing a substrate in a chamber, providing an energized etchant gas in the chamber to etch the substrate, providing a burst of energized cleaning gas in the chamber to clean the chamber surfaces, the energized cleaning gas comprising one or more of (i) carbon and fluorine species, and (ii) sulfur and fluorine species, and after the burst of energized cleaning gas, removing the substrate from the chamber.
In another aspect of the invention, a substrate processing method comprises placing the substrate in a process zone of a chamber and providing in the process zone an energized process gas comprising an etchant gas and a cleaning gas in a volumetric flow ratio of cleaning gas to etchant gases sufficiently high to at least partially remove etchant residue deposited on surfaces in the chamber, the etchant gas comprising a first halogen containing gas and one or more of a second halogen containing gas, N2, O2, and Hexe2x80x94O2.
In another aspect of the invention, a substrate processing method comprises placing the substrate in a process zone of a chamber; providing in the process zone an energized process gas comprising etchant gas to etch the substrate, the etchant gas comprising a first halogen and one or more of N2, a second halogen, O2, and Hexe2x80x94O2; and providing in the process zone a burst of energized cleaning gas while the substrate is being etched, the volumetric flow ratio of cleaning gas to etchant gases being sufficiently high to at least partially remove etchant residue deposited on surfaces in the chamber.
In another aspect of the invention, a substrate processing method comprises placing the substrate in the etching chamber, providing an energized process gas in the etching chamber in a volumetric flow rate selected to etch the substrate and at least partially remove etchant residue formed on the chamber surfaces, the process gas comprising carbon and fluorine species, and repeating the steps.
In another aspect of the invention, a substrate processing method comprises placing the substrate in the etching chamber, providing an energized process gas in the etching chamber in a volumetric flow rate selected to etch the substrate and at least partially remove etchant residue formed on the chamber surfaces, the process gas comprising sulfur and fluorine species, and repeating the steps.
In another aspect of the invention, a substrate processing method comprises placing a substrate in a chamber, providing an energized etchant gas in the chamber to etch the substrate, and providing a burst of energized cleaning gas in the chamber while the substrate is being etched to at least partially clean the chamber surfaces, the energized cleaning gas comprising carbon and fluorine species.
In another aspect of the invention, a substrate processing method comprises placing a substrate in a chamber, providing an energized etchant gas in the chamber to etch the substrate, and providing a burst of energized cleaning gas in the chamber while the substrate is being etched to at least partially clean the chamber surfaces, the energized cleaning gas comprising sulfur and fluorine species.
The present invention provides a method of etching a substrate in an etching chamber, that reduces or entirely eliminates the etch residues on the chamber surfaces and provides highly consistent and reproducible etching performance. In the method a substrate is etched and simultaneously, the etching chamber is cleaned off etch residue. A substrate is placed in the chamber, and a plasma is formed from process gas introduced into the chamber to simultaneously etch the substrate, and clean etch residue deposited on the chamber surfaces. The process gas comprises (i) etchant gas for etching the substrate thereby forming etch residue on chamber surfaces, and (ii) cleaning gas for cleaning the etch residue formed on the chamber surfaces, the volumetric flow ratio of cleaning gas to etchant gas selected so that the etch residue is substantially entirely removed from the chamber surfaces upon completion of the etch process.
The method is useful for etching metal silicide, silicon nitride, polysilicon, or monocrystalline silicon on a substrate, while simultaneously cleaning the etching chamber of silicon dioxide containing etch residue. In this method, a plasma is generated from one or more process gases introduced into the chamber to etch the substrate and clean the etch residue on the etching chamber surfaces. The process gas comprises (i) etchant gases for etching metal silicide, polysilicon, or silicon on the substrate thereby forming silicon dioxide etch residue on the etching chamber surfaces, and (ii) cleaning gas for removing the silicon dioxide etch residue on the etching chamber surfaces. The volumetric flow ratio of cleaning gas to etchant gas selected to remove substantially all the silicon dioxide etch residue from the chamber surfaces upon completion of the etch process.
In one example of the present process, a substrate comprising silicon-containing material (metal silicide, monocrystalline silicon, polycrystalline silicon, silicon nitride or silicon oxide) is etched using a plasma of process gas comprising Cl2, N2, and CF4, in a volumetric flow ratio selected to remove substantially all the etch residue formed on the chamber surfaces upon completion of the etching process. Preferably, the volumetric flow ratio of Cl2, N2, and CF4, is selected to remove substantially all the etchant residue generated by etching at least 2000 substrates in the chamber, without performing a separate cleaning step for cleaning the chamber. The ratio of the volumetric flow ratio of CF4: (Cl2+N2) is more preferably from about 1:20 to about 1:1. In another example, the process uses a process gas comprising Cl2, N2, and SF6, preferably, the volumetric flow ratio of SF6: (Cl2+N2) being from about 1:20 to about 1:1. In yet another example, a suitable process gas comprises Cl2, N2, and NF3, preferably, the volumetric flow ratio of NF3: (Cl2+N2) being from about 1:20 to about 1:1.
The method is particularly useful for etching substrates comprising multiple layers, for example, for etching polycide structures composed of tungsten silicide and polysilicon layers, or for etching silicon nitride layers deposited over silicon dioxide layersxe2x80x94while simultaneously cleaning the etching chamber of silicon dioxide containing etch residue. The multiple layers are etched in a multiple stage process. In a first etching stage, a first etchant gas is introduced into the chamber and a plasma generated from the first etchant gas for etching the first layer. In a second etching stage, a second etchant gas is introduced into the chamber and a plasma is generated from the second etchant gas for etching the second layer. In one or more these stages, cleaning gas is added to the etchant gas to generate a cleaning plasma that removes all the silicon dioxide etch residue formed on the etching chamber surfaces in both of the etching stages.
In another aspect, the method of the present invention is useful for fabricating a semiconductor substrate. In this method, a process gas comprising etchant gases for etching the substrate, is introduced into the chamber, and a plasma is generated from the etchant gas to etch the substrate. A burst of cleaning gas is added to the process gas while the substrate is still being etched, to clean the chamber surfaces. The cleaning gas is added for a sufficient time, and the volumetric flow ratio of cleaning gas to etchant gases is sufficiently high, to remove substantially all the etch residue formed or deposited during the etching process.